In conventional Public Switch Telephone Networks (PSTN) and Integrated Services Digital Networks (ISDN), for example, up till now the overwhelming majority of residential and office subscribers have a wired connection from the subscriber premises to a public local exchange. These subscriber connections, which may run via an intermediate concentrator, are referred to as the local loop.
The installation of such wired links all the way down to the subscriber premises is both time consuming and involves substantial networking costs, apart from troubles caused by the interruption of streets and pavements. Therefore, there is a growing interest in replacing the wired local loop by a so-called wireless local loop, i.e. using radio technology as an alternative for or as a replacement of the copper wires down to the subscriber premises. This is not only of interest for the present network operators in case of expansion or renovation of the existing public telecommunication network but, in particular, for new operators which would like to provide competitive public telecommunication services, such as a public telephone service. The concept of wireless public subscriber connections is called RLL or WLL.
Within the concept of RLL, two basic systems can be distinguished: Fixed RLL (FRLL) and Mobile RLL (MRLL). In the FRLL system, the subscriber is provided with an ordinary telephone socket, however connected to a radio transceiver, also called Fixed Access Unit (FAU) or Wireless Fixed Access Unit (WFAU). Via this FAU/WFAU a radio link is established with a so-called base station or radio access unit, which provides access to the PSTN/ISDN. In the MRLL concept, the subscriber is provided with a portable cordless or mobile radio telephone handset, by which, via the radio access unit access to the PSTN/ISDN can be established.
Mixed concepts are also possible, i.e. FRLL providing mobility in the subscriber premises, also called Cordless In The Home (CITH) and residential or neighborhood mobility, also called Cordless In The Neighborhood (CITN). In some countries, governmental regulations prevent the established telephone operators from offering local mobility in the present PSTN/ISDN. In such cases, it is very attractive for a second or third operator to offer both fixed and mobile or cordless access to the PSTN/ISDN.
The advantages of wireless local loop connections in the PSTN/ISDN network are numerous, ranging from short installation times, increased flexibility and improved operation and maintenance of the network to the opportunity of providing local subscriber mobility to the PSTN/ISDN.
International Patent Application WO 94/19877 discloses an RLL system based on existing business cordless technology, such as designated CT2, CT3 and Digital Enhanced Cordless Telecommunications (DECT). These cordless communication systems have been developed for use in picocells (having a range from the radio access unit to the cell boundary of a few meters), nanocells (up to 10 m) and microcells (10 to 400 m for pedestrians and 300 m to 2 km for vehicles).
The non-prepublished International Patent Application PCT/EP95/04509 discloses an RLL system comprising a number of geographically spread radio access units or radio access units based on the above cordless communication techniques, in particular DECT, providing coverage in sectors for use in minicells (500 m to 3 km) and macrocells (up to 5 km).
Other types of communication systems having wired connections to a PSTN/ISDN are the well-known cellular mobile telephone and data transmission systems. A typical cellular mobile communication system comprises mobile radio subscriber units, a plurality of radio base stations, each providing service to a geographical area or cell, and radio exchanges or mobile telephone switching offices (MTSO) to which a number of base stations are connected. The MTSO are, in turn, coupled to a PSTN/ISDN for completing transmissions, such as telephone calls, between mobile radio subscribers and landline subscribers.
Analogue cellular systems, such as designated AMPS, ETACS, NMT-450 and NMT-900 have been deployed throughout the world. Digital cellular systems are designated IS54B in North America and the pan-European GSM system. These systems, and others, are described, for example, in the book titled "Cellular Radio Systems", by Balston et al., published by Artech House, Norwood, Mass., 1993.
First generation cellular mobile networks provide service to macrocells, and large cells (5 to 35 km), with some satellite cells (&gt;500 km). An important problem in wireless cellular communication is to provide full coverage cost effectively. This has lead to the splitting of cells in dense traffic areas, adding microcells and minicells overlaid by a macrocell structure. The overlaying macrocells serve low-traffic areas and cell crossings by mobile subscribers.
Future cellular mobile networks will also have picocells and nanocells often in clusters of street microcells, with each cluster overlaid by a macrocell. In a typical cell overlay configuration, each microcell has its own base station providing service to the corresponding cell, whereas the several base stations are wired to a concentrator or access unit which is, in turn, coupled to a MTSO.
There are various tools available for the planning of radio communication networks. In the case of present cellular systems, the main problem to be solved is the efficient use of limited frequency or communication channel resources. Reference is made, inter alia, to International Patent Application WO 90/10342 and European Patent Application 0,559,949. These known planning tools require, however, detailed geographical information on the coverage region and/or signal strength, coverage and interference measurements.
Different from the present cellular radio communication systems, in cordless systems such as DECT frequency planning is not an essential issue. DECT is a low power, high capacity Multi Carrier/Time Division Multiple Access/Time Division Duplex (MC/TDMA/TDD) digital radio access technique, providing ten radio carriers, each divided into 24 time-slots which serve 12 duplex communication channels, called a frame. The communication channels are continuously adaptively selected. A communication channel, when occupied, is individual to a radio link connection between the base station and a particular remote telecommunication unit. This type of access technique is known as Continuous Dynamic Channel Allocation (CDCA).
However, due to the relatively low transmission power of the cordless equipment, compared to the present cellular systems, cost effective coverage planning is an important issue for cordless telecommunication systems.
European Patent Application 0,624,961 discloses a method for the planning of cordless telephone systems in indoor environments, such as offices, production halls etc. This method relates to the calculation of the number of base stations required for providing a required grade of service. The method is, however, not quite suitable for use in telecommunication systems operating in outdoor environments such as RLL or WLL communication networks.
An essential requirement for RLL or WLL network systems, for example, is to enable installations which are economic as to capacity and power. That is to say, the various components of the system have to be designed such that an optimum between geographical coverage, range, communication capacity and installation costs can be achieved, in order to provide competitive wireless connections.
Accordingly, there is a need for a planning tool to provide an estimate on the system requirements which allows a potential operator and/or a system manufacturer to calculate in advance is system costs. This, however, without the need for detailed information of the geographic configuration of the area of interest, e.g. in the form of a blueprint or topographic chart, satellite observations, or specialist knowledge for providing field strength measurements and the like.